Method for operating a medical  robotic system by stopping movement of a surgical instrument about a pivot point or issuing a warning if the pivot point moves beyond a thershold value

ABSTRACT

A system for performing minimally invasive cardiac procedures. The system includes a pair of surgical instruments that are coupled to a pair of robotic arms. The instruments have end effectors that can be manipulated to hold and suture tissue. The robotic arms are coupled to pair of master handles by a controller. The handles can be moved by the surgeon to produce a corresponding movement of the end effectors. The controller controls and limits movement of robotic arms relative to the patient.

REFERENCE TO CROSS-RELATED APPLICATIONS

This is a continuation of application Ser. No. 10/310,405 filed Dec. 4,2002, which is a continuation of Ser. No. 09/000,934, filed on Dec. 30,1997, U.S. Pat. No. 6,905,491, which is a continuation of applicationSer. No. 08/603,543, filed on Feb. 20, 1996, U.S. Pat. No. 5,762,458,and a continuation-in-part of application Ser. No. 08/903,914 filed onJul. 31, 1997, U.S. Pat. No. 5,815,640, which is a continuation ofapplication Ser. No. 08/613,866, filed on Mar. 11, 1996, U.S. Pat. No.5,907,664, which is a continuation of application Ser. No. 08/072,982,filed on Jun. 3, 1993, U.S. Pat. No. 5,524,180, which is acontinuation-in part of application Ser. No. 08/005,604 filed on Jan.19, 1993, abandoned, which is a continuation-in-part of application Ser.No. 07/927,801, filed on Aug. 10, 1992 abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a system and method for performingminimally invasive cardiac procedures.

2. Description of Related Art

Blockage of a coronary artery may deprive the heart of the blood andoxygen required to sustain life. The blockage may be removed withmedication or by an angioplasty. For severe blockage a coronary arterybypass graft (CABG) is performed to bypass the blocked area of theartery. CABG procedures are typically performed by splitting the sternumand pulling open the chest cavity to provide access to the heart. Anincision is made in the artery adjacent to the blocked area. Theinternal mammary artery (IMA) is then severed and attached to the arteryat the point of incision. The IMA bypasses the blocked area of theartery to again provide a full flow of blood to the heart.-‘Splittingthe sternum and opening the chest cavity can create a tremendous traumaon the patient. Additionally, the cracked sternum prolongs the recoveryperiod of the patient.

There have been attempts to perform CABG procedures without opening thechest cavity. Minimally invasive procedures are conducted by insertingsurgical instruments and an endoscope through small incision in the skinof the patient. Manipulating such instruments can be awkward,particularly when suturing a graft to a artery. It has been found that ahigh level of dexterity is required to accurately control theinstruments. Additionally, human hands typically have at least a minimalamount of tremor. The tremor further increases the difficulty ofperforming minimal invasive cardiac procedures. It would be desirable toprovide a system for effectively performing minimally invasive coronaryartery bypass graft procedures.

BRIEF SUMMARY OF THE INVENTION

The present invention is a system for performing minimally invasivecardiac procedures. The system includes a pair of surgical instrumentsthat are coupled to a pair of robotic arms. The instruments have endeffectors that can be manipulated to hold and suture tissue. The roboticarms are coupled to a pair of master handles by a controller. Thehandles can be moved by the surgeon to produce a corresponding movementof the end effectors. The movement of the handles is scaled so that theend effectors have a corresponding movement that is different, typicallysmaller, than the movement performed by the hands of the surgeon. Thescale factor is adjustable so that the surgeon can control theresolution of the end effector movement. The movement of the endeffector can be controlled by an input button, so that the end effectoronly moves when the button is depressed by the surgeon. The input buttonallows the surgeon to adjust the position of the handles without movingthe end effector, so that the handles can be moved to a more comfortableposition. The system may also have a robotically controlled endoscopewhich allows the surgeon to remotely view the surgical site. A cardiacprocedure can be performed by making small incisions in the patient'sskin and inserting the instruments and endoscope into the patient. Thesurgeon manipulates the handles and moves the end effectors to perform acardiac procedure such as a coronary artery bypass graft.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the present invention will become morereadily apparent to those ordinarily skilled in the art after reviewingthe following detailed description and accompanying drawings, wherein:

FIG. 1 is a perspective view of a minimally invasive surgical system ofthe present invention;

FIG. 2 is a schematic of a master of the system;

FIG. 3 is a schematic of a slave of the system;

FIG. 4 is a schematic of a control system of the system;

FIG. 5 is a schematic showing the instrument in a coordinate frame;

FIG. 6 is a schematic of the instrument moving about a pivot point;

FIG. 7 is an exploded view of an end effector of the system;

FIG. 8 is a top view of a master handle of the system;

FIG. 8 a is a side view of the master handle;

FIGS. 9-10A-I are illustrations showing an internal mammary artery beinggrafted to a coronary artery.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings more particularly by reference numbers, FIG. 1shows a system 10 that can perform minimally invasive surgery. In thepreferred embodiment, the system 10 is used to perform a minimallyinvasive coronary artery bypass graft (MI-CABG) and other anastomosticprocedures. Although a MI-CABG procedure is shown and described, it isto be understood that the system may be used for other surgicalprocedures. For example, the system can be used to suture any pair ofvessels.

The system 10 is used to perform a procedure on a patient 12 that istypically lying on an operating table 14. Mounted to the operating table14 is a first articulate arm 16, a second articulate arm 18 and a thirdarticulate arm 20. The articulate arms 16-20 are preferably mounted tothe table so that the arms are at a same reference plane as the patient.Although three articulate arms are shown and described, it is to beunderstood that the system may have any number of arms.

The first and second articulate arms 16 and 18 each have a surgicalinstrument 22 and 24 coupled to a robotic arm 26. The third articulatearm 20 has an endoscope 28 that is held by a robotic arm 26. Theinstruments 22 and 24, and endoscope 28 are inserted through incisionscut into the skin of the patient. The endoscope has a camera 30 that iscoupled to a television monitor 32 which displays images of the internalorgans of the patient.

The robotic arms 26 each have a linear motor 34, a first rotary motor 36and a second rotary motor 38. The robotic arms 26 also have a pair ofpassive joints 40 and 42. The articulate arm 20 also have a worm gear 44and means to couple the instruments 22 and 24, and endoscope 28 to therobotic arm 26. The first, second, and third articulate arms are coupledto a controller 46 which can control the movement of the arms.

The controller 46 is connected to an input device 48 such as a footpedal that can be operated by a surgeon to move the location of theendoscope and view a different portion of the patient by depressing acorresponding button(s) of the foot pedal 48. The controller 46 receivesthe input signals from the foot pedal 48 and moves the robotic arm 26and endoscope 28 in accordance with the input commands of the surgeon.The robotic arms may be devices that are sold by the assignee of thepresent invention, Computer Motion, Inc. of Goleta, Calif., under thetrademark AESOP. The system is also described in allowed U.S.application Ser. No. 08/305,415, which is hereby incorporated byreference. Although a foot pedal 46 is shown and described, it is to beunderstood that the system may have other input means such as a handcontroller, or a speech recognition interface.

The instruments 22 of the first 16 and second 18 articulate arms arecontrolled by a pair of master handles 50 and 52 that can be manipulatedby the surgeon. The handles 50 and 52, and arms 16 and 18, have amaster-slave relationship so that movement of the handles produces acorresponding movement of the surgical instruments. The handles 50 and52 may be mounted to a portable cabinet 54. A second television monitor56 may be placed onto the cabinet 54 and coupled to the endoscope 28 sothat the surgeon can readily view the internal organs of the patient.The handles 50 and 52 are also coupled to the controller 46. Thecontroller 46 receives input signals from the handles 50 and 52,computes a corresponding movement of the surgical instruments, andprovides output signals to move the robotic arms and instruments.

Each handle has multiple degrees of freedom provided by the variousjoints Jm1-Jm5 depicted in FIG. 2. Joints Jm1 and Jm2 allow the handleto rotate about a pivot point of the cabinet 54. Joint Jm3 allows thesurgeon to move the handle into and out of the cabinet 54 in a linearmanner. Joint Jm4 allows the surgeon to rotate the master handle about alongitudinal axis of the handle. The joint Jm5 allows a surgeon to openand close a gripper. Each joint Jm1-Jm5 has a position sensor whichprovides feedback signals that correspond to the relative position ofthe handle. The position sensors may be potentiometers, or any otherfeedback device, that provides an electrical signal which corresponds toa change of position.

FIG. 3 shows the various degrees of freedom of each articulate arm 16and 18. The joints Js1, Js2 and Js3 correspond to the linear motor androtary motors of the robotic arms 26, respectively. The joints Js4 andJs5 correspond to the passive joints 40 and 42 of the arms 26. The jointJs6 may be a motor which rotates the surgical instruments about thelongitudinal axis of the instrument. The joint Js7 may be a pair offingers that can open and close. The instruments 22 and 24 move about apivot point P located at the incision of the patient.

FIG. 4 shows a schematic of a control system that translates a movementof a master handle into a corresponding movement of a surgicalinstrument. In accordance with the control system shown in FIG. 4, thecontroller 46 computes output signals for the articulate arms so thatthe surgical instrument moves in conjunction with the movement of thehandle. Each handle may have an input button 58 which enables theinstrument to move with the handle. When the input button 58 isdepressed the surgical instrument follows the movement of the handle.When the button 58 is released the instrument does not track themovement of the handle. In this manner the surgeon can adjust or“ratchet” the position of the handle without creating a correspondingundesirable movement of the instrument. The “ratchet” feature allows thesurgeon to continuously move the handles to more desirable positionswithout altering the positions of the arms. Additionally, because thehandles are constrained by a pivot point the ratchet feature allows thesurgeon to move the instruments beyond the dimensional limitations ofthe handles. Although an input button is shown and described, it is tobe understood that the surgical instrument may be activated by othermeans such as voice recognition. The input button may be latched so thatactivation of the instrument toggles between active and inactive eachtime the button is depressed by the surgeon.

When the surgeon moves a handle, the position sensors provide feedbacksignals M1-M5 that correspond to the movement of the joints Jm1-Jm5,respectively. The controller 46 computes the difference between the newhandle position and the original handle position in computation block 60to generate incremental position values ΔM1-ΔM5.

The incremental position values ΔM1-ΔM5 are multiplied by scale factorsS1-S5, respectively in block 62. The scale factors are typically set atless than one so that the movement of the instrument is less than themovement of the handle. In this manner the surgeon can produce very finemovements of the instruments with relatively coarse movements of thehandles. The scale factors S1-S5 are variable so that the surgeon canvary the resolution of instrument movement. Each scale factor ispreferably individually variable so that the surgeon can more finelycontrol the instrument in certain directions. By way of example, bysetting one of the scale factors at zero the surgeon can prevent theinstrument from moving in one direction. This may be advantageous if thesurgeon does not want the surgical instrument to contact an organ orcertain tissue located in a certain direction relative to the patient.Although scale factors smaller than a unit one described, it is to beunderstood that a scale factor may be greater than one. For example, itmay be desirable to spin the instrument at a greater rate than acorresponding spin of the handle.

The controller 46 adds the incremental values ΔM1-ΔM5 to the initialjoint angles Mj1-Mj5 in adder element 64 to provide values Mr1-Mr5. Thecontroller 46 then computes desired slave vector calculations incomputation block 66 in accordance with the following equations.

Rdx=Mr3·sin(Mr1)·cos(Mr2)+Px

Rdy=Mr3·sin(Mr1)·sin(Mr2)+Py

Rdz=Mr3·cos(Mr1)+Pz

Sdr=Mr4

Sdg=Mr5

where;

-   -   Rdx, y, z=the new desired position of the end effector of the        instrument.    -   Sdr=the angular rotation of the instrument about the instrument        longitudinal axis.    -   Sdg=the amount of movement of the instrument fingers.    -   Px, y, z=the position of the pivot point P.

The controller 46 then computes the movement of the robotic arm 26 incomputational block 68 in accordance with the following equations.

Jsd 1 = Rdz ${{Jsd}\; 3} = {p - {\cos^{- 1}\begin{matrix}é \\\hat{e} \\\hat{e} \\e\end{matrix}\frac{{Rdx}^{2} + {Rdy}^{2} - {L\; 1^{2}} - {L\; 2^{2}}}{2L\; 1 \times L\; 2}\begin{matrix}ù \\ú \\ú \\u\end{matrix}}}$Jsd 2 = tan⁻¹(Rdy/Rdx) + D  for  Jsd 3  £  0Jsd 2 = tan⁻¹(Rdy/Rdx) − D  for  Jsd 3 > 0$D = {\cos^{- 1}\begin{matrix}é \\\hat{e} \\\hat{e} \\\hat{e} \\e\end{matrix}\frac{{Rdx}^{2} + {Rdy}^{2} - {L\; 1^{2}} - {L\; 2^{2}}}{2 \times L\; 1\sqrt{{Rdx}^{2} + {Rdy}^{2}}}\begin{matrix}ù \\ú \\ú \\ú \\u\end{matrix}}$ Jsd 6 = Mr 4 Jsd 7 = Mr 5

where;

-   -   Jsd1=the movement of the linear motor.    -   Jsd2=the movement of the first rotary motor.    -   Jsd3=the movement of the second rotary motor.    -   Jsd6=the movement of the rotational motor.    -   Jsd7=the movement of the gripper.    -   L1=the length of the linkage arm between the first rotary motor        and the second rotary motor.    -   L2=the length of the linkage arm between the second rotary motor        and the passive joints.

The controller provides output signals to the motors to move the arm andinstrument in the desired location in block 70. This process is repeatedfor each movement of the handle.

The master handle will have a different spatial position relative to thesurgical instrument if the surgeon releases the input button and movesthe handle. When the input button 58 is initially depressed, thecontroller 46 computes initial joint angles Mj1-Mj5 in computationalblock 72 with the following equations.

Mj 1 = tan⁻¹(ty/tx) Mj 2 = tan⁻¹(d/tz) Mj 3 = D Mj 4 = Js 6Mj 5 = Js 7 $d = \sqrt{{tx}^{2} + {ty}^{2}}$${tx} = {{\frac{{Rsx} - {Px}}{D}\mspace{20mu} {ty}} = {{\frac{{Rsy} - {Py}}{D}\mspace{20mu} {tz}} = \frac{{Rsz} - {Pz}}{D}}}$$D = \sqrt{\left( {{rsx} - {Px}} \right)^{2} + \left( {{Rsy} - {Py}} \right)^{2} + \left( {{Rsz} - {Pz}} \right)^{2}}$

The forward kinematic values are computed in block 74 with the followingequations.

Rsx=L1·cos(Js2)+L2·cos(Js2+Js3)

Rsy=L1·cos(Js2)−L2·sin(Js2+Js3)

Rsz=J1

The joint angles Mj are provided to adder 64. The pivot points Px, Pyand Pz are computed in computational block 76 as follows. The pivotpoint is calculated by initially determining the original position ofthe intersection of the end effector and the instrument PO, and the unitvector Uo which has the same orientation as the instrument. The positionP(x, y, z) values can be derived from various position sensors of therobotic arm. Referring to FIG. 5 the instrument is within a firstcoordinate frame (x, y, z) which has the angles θ4 and θ5. The unitvector Uo is computed by the transformation matrix:

$U_{O} = {\begin{bmatrix}{\cos \; \Theta_{5}} & 0 & {{- \sin}\; \Theta_{5}} \\{{- \sin}\; \Theta_{4}\sin \; \Theta_{5}} & {\cos \; \Theta_{4}} & {{- \sin}\; \Theta_{4}\cos \; \Theta_{5}} \\{\cos \; \Theta_{4}\sin \; \Theta_{5}} & {\sin \; \Theta_{4}} & {\cos \; \Theta_{4}}\end{bmatrix}\begin{bmatrix}0 \\0 \\{- 1}\end{bmatrix}}$

After each movement of the end effector an angular movement of theinstrument Δθ is computed by taking the arcsin of the cross-product ofthe first and second unit vectors Uo and U1 of the instrument inaccordance with the following line equations Lo and L1.

Δθ=arcsin(|T|)

T=Uo×Ul

where;

-   -   T=a vector which is a cross-product of unit vectors Uo and U1.

The unit vector of the new instrument position U1 is again determinedusing the positions sensors and the transformation matrix describedabove. If the angle Δθ is greater than a threshold value, then anewpivot point is calculated and Uo is set to U1. As shown in FIG. 6, thefirst and second instrument orientations can be defined by the lineequations Lo and L1:

xo=Mx0·Zo+Cxo

yo=Myo·Zo+Cyo  Lo

x1=Mx1·Z1+Cx1

y1=My1·Z1+Cy1  L1

where;

-   -   Zo=a Z coordinate along the line Lo relative to the z axis of        the first coordinate system.    -   Z1=a Z coordinate along the line L1 relative to the z axis of        the first coordinate system.    -   Mxo=a slope of the line Lo as a function of Zo.    -   Myo=a slope of the line Lo as a function of Zo.    -   Mx1=a slope of the line L1 as a function of Z1.    -   My1=a slope of the line L1 as a function of Z1.    -   Cxo=a constant which represents the intersection of the line Lo        and the x axis of the first coordinate system.    -   Cyo=a constant which represents the intersection of the line Lo        and the y axis of the first coordinate system.    -   Cx1=a constant which represents the intersection of the L1 and        the x axis of the first coordinate system.    -   Cy1=a constant which represents the intersection of the line L1        and the y axis of the first coordinate system.

The slopes are computed using the following algorithms:

Mxo=Uxo/Uzo

Myo=Uyo/Uzo

Mx1=Ux1/Uzi

My1=Uy1/Uz1

Cx0=Pox−Mx1·Poz

Cy0=Poy−My1·Poz

Cx1=P1x−Mx1·P1z

Cy1=P1y−My1·P1z

where;

-   -   Uo (x, y and z)=the unit vectors of the instrument in the first        position within the first coordinate system.    -   U1 (x, y and z)=the unit vectors of the instrument in the second        position within the first coordinate system.    -   Po (x, y and z)=the coordinates of the intersection of the end        effector and the instrument in the first position within the        first coordinate system.    -   P1 (x, y and z)=the coordinates of the intersection of the end        effector and the instrument in the second position within the        first coordinate system.

To find an approximate pivot point location, the pivot points of theinstrument in the first orientation Lo (pivot point Ro) and in thesecond orientation L1 (pivot point R1) are determined, and the distancehalf way between the two points Ro and R1 is computed and stored as thepivot point R_(ave) of the instrument. The pivot point R_(ave) isdetermined by using the cross-product vector T.

To find the points Ro and R1 the following equalities are set to definea line with the same orientation as the vector T that passes throughboth Lo and L1.

tx=Tx/Tz

ty=Ty/Tz

where;

-   -   tx=the slope of a line defined by vector T relative to the Z-x        plane of the first coordinate system.    -   ty=the slope of a line defined by vector T relative to the Z-y        plane of the first coordinate system.    -   Tx=the x component of the vector T.    -   Ty=the y component of the vector T.    -   Tz=the z component of the vector T.

Picking two points to determine the slopes Tx, Ty and Tz (e.g. Tx=x1−xo,Ty=y1−yo and Tz=z1−z0) and substituting the line equations Lo and L1,provides a solution for the point coordinates for Ro (xo, yo, zo) and R1(x1, y1, z1) as follows.

zo=((Mx1−tx)z1+Cx1−Cxo)/(Mxo−tx)

z1=((Cy1−Cyo)(Mxo−tx)−(Cx1−Cxo)(Myo−ty))/((Myo−ty)(Mx1−tx)−(My1−ty)(Mxo−tx))

yo=Myo·zo+Cyo

y1=My1·z1+Cy1

xo=Mxo·zo+Cxo

x1=Mx1·z1+Cx1

The average distance between the pivot points Ro and R1 is computed withthe following equation and stored as the pivot point of the instrument.

R _(ave)=((x1+xo)/2,(y1+yo)/2,(z1+zo)/2)

The pivot point can be continually updated with the above describedalgorithm routine. Any movement of the pivot point can be compared to athreshold value and a warning signal can be issued or the robotic systemcan become disengaged if the pivot point moves beyond a set limit. Thecomparison with a set limit may be useful in determining whether thepatient is being moved, or the instrument is being manipulated outsideof the patient, situations which may result in injury to the patient orthe occupants of the operating room.

To provide feedback to the surgeon the fingers of the instruments mayhave pressure sensors that sense the reacting force provided by theobject being grasped by the end effector. Referring to FIG. 4, thecontroller 46 receives the pressure sensor signals Fs and generatescorresponding signals Cm in block 78 that are provided to an actuatorlocated within the handle. The actuator provides a correspondingpressure on the handle which is transmitted to the surgeon's hand. Thepressure feedback allows the surgeon to sense the pressure being appliedby the instrument. As an alternate embodiment, the handle may be coupledto the end effector fingers by a mechanical cable that directlytransfers the grasping force of the fingers to the hands of the surgeon.

FIG. 7 shows a preferred embodiment of an end effector 80. The endeffector 80 includes a tool 82 that is coupled to an arm 84 by a sterilecoupler 86. The tool 82 has a first finger 88 that is pivotallyconnected to a second finger 90. The fingers can be manipulated to holdobjects such as tissue or a suturing needle. The inner surface of thefingers may have a texture to increase the friction and grasping abilityof the tool. The first finger 88 is coupled to a rod 92 that extendsthrough a center channel 94 of the tool 82. The tool 82 may have anouter sleeve 96 which cooperates with a spring biased ball quickdisconnect fastener 98 of the sterile coupler 86. The quick disconnectallows tools other than the finger grasper to be coupled to an arm. Forexample, the tool 82 may be decoupled from the coupler and replaced by acutting tool. The coupler 86 allows the surgical instruments to beinterchanged without having to re-sterilize the arm each time aninstrument is plugged into the arm.

The sterile coupler 86 has a slot 100 that receives a pin 102 of the arm84. The pin 102 locks the coupler 86 to the arm 84. The pin 102 can bereleased by depressing a spring biased lever 104. The sterile coupler 86has a piston 106 that is attached to the tool rod and in abutment withan output piston 108 of a load cell 110 located within the arm 84.

The load cell 110 is mounted to a lead screw nut 112. The lead screw nut112 is coupled to a lead screw 114 that extends from a gear box 116. Thegear box 116 is driven by a reversible motor 118 that is coupled to anencoder 120. The entire arm 82 is rotated by a motor drive worm gear122. In operation, the motor receives input commands from the controller46 and activates, accordingly. The motor 118 rotates the lead screw 114which moves the lead screw nut 112 and load cell 110 in a linear manner.Movement of the load cell 110 drives the coupler piston 106 and tool rod92, which rotate the first finger 88. The load cell 110 senses thecounteractive force being applied to the fingers and provides acorresponding feedback signal to the controller 46. The arm 84 may becovered with a sterile drape 124 so that the arm does not have to besterilized after each surgical procedure.

FIGS. 8 and 8 a show a preferred embodiment of a master handle assembly130. The assembly 130 includes a master handle 132 that is coupled to anarm 134. The master handle 132 may be coupled to the arm 134 by a pin136 that is inserted into a corresponding slot 138 in the handle 132.The handle 132 has a control button 140 that can be depressed by thesurgeon. The control button 140 is coupled to a switch 142 by a shaft144. The control button 140 corresponds to the input button 58 shown inFIG. 4, and activates the movement of the end effector.

The master handle 132 has a first gripper 146 that is pivotallyconnected to a second stationary gripper 148. Rotation of the firstgripper 146 creates a corresponding linear movement of a handle shaft150. The handle shaft 150 moves a gripper shaft 152 that is coupled to aload cell 154 by a bearing 156. The load cell 154 senses the amount ofpressure being applied thereto and provides an input signal to thecontroller 46. The controller 46 then provides an output signal to movethe fingers of the end effector.

The load cell 154 is mounted to a lead screw nut 158 that is coupled toa lead screw 160. The lead screw 160 extends from a reduction box 162that is coupled to a motor 164 which has an encoder 166. The controller46 of the system receives the feedback signal of the load cell 110 inthe end effector and provides a corresponding command signal to themotor to move the lead screw 160 and apply a pressure on the gripper sothat the surgeon receives feedback relating to the force being appliedby the end effector. In this manner the surgeon has a “feel” foroperating the end effector.

The handle is attached to a swivel housing 168 that rotates aboutbearing 170. The swivel housing 168 is coupled to a position sensor 172by a gear assembly 174. The position sensor 172 may be a potentiometerwhich provides feedback signals to the controller 46 that correspond tothe relative position of the handle. The swivel movement is translatedto a corresponding spin of the end effector by the controller androbotic arm.

The arm 134 may be coupled to a linear bearing 176 and correspondingposition sensor 178 which allow and sense linear movement of the handle.The linear movement of the handle is translated into a correspondinglinear movement of the end effector by the controller and robotic arm.The arm can pivot about bearings 180, and be sensed by position sensor182 located in a stand 184. The stand 184 can rotate about bearing 186which has a corresponding position sensor 188. The arm rotation istranslated into corresponding pivot movement of the end effector by thecontroller and robotic arm.

A human hand will have a natural tremor typically resonating between6-12 hertz. To eliminate tracking movement of the surgical instrumentswith the hand tremor, the system may have a filter that filters out anymovement of the handles that occurs within the tremor frequencybandwidth. Referring to FIG. 4, the filter 184 may filter analog signalsprovided by the potentiometers in a frequency range between 6-12 hertz.

As shown in FIGS. 9 and 10A-I the system is preferably used to perform acardiac procedure such as a coronary artery bypass graft (CABG). Theprocedure is performed by initially cutting three incisions in thepatient and inserting the surgical instruments 22 and 24, and theendoscope 26 through the incisions. One of the surgical instruments 22holds a suturing needle and accompanying thread when inserted into thechest cavity of the patient. If the artery is to be grafted with asecondary vessel, such as a saphenous vein, the other surgicalinstrument 24 may hold the vein while the end effector of the instrumentis inserted into the patient.

The internal mammary artery (IMA) may be severed and moved by one of theinstruments to a graft location of the coronary artery. The coronaryartery is severed to create an opening in the artery wall of a size thatcorresponds to the diameter of the IMA. The incision(s) may be performedby a cutting tool that is coupled to one of the end effectors andremotely manipulated through a master handle. The arteries are clampedto prevent a blood flow from the severed mammary and coronary arteries.The surgeon manipulates the handle to move the IMA adjacent to theopening of the coronary artery. Although grafting of the IMA is shownand described, it is to be understood that another vessel such as asevered saphaneous vein may be grafted to bypass a blockage in thecoronary artery.

Referring to FIGS. 10A-I, the surgeon moves the handle to manipulate theinstrument into driving the needle through the IMA and the coronaryartery. The surgeon then moves the surgical instrument to grab and pullthe needle through the coronary and graft artery as shown in FIG. 10B.As shown in FIG. 10C, the surgical instruments are then manipulated totie a suture at the heel of the graft artery. The needle can then beremoved from the chest cavity. As shown in FIGS. 10D-F, a new needle andthread can be inserted into the chest cavity to suture the toe of thegraft artery to the coronary artery. As shown in FIG. 10H-I, new needlescan be inserted and the surgeon manipulates the handles to createrunning sutures from the heel to the toe, and from the toe to the heel.The scaled motion of the surgical instrument allows the surgeon toaccurately move the sutures about the chest cavity. Although a specificgraft sequence has been shown and described, it is to be understood thatthe arteries can be grafted with other techniques. In general the systemof the present invention may be used to perform any minimally invasiveanastomostic procedure.

While certain exemplary embodiments have been described and shown in theaccompanying drawings, it is to be understood that such embodiments aremerely illustrative of and not restrictive on the broad invention, andthat this invention not be limited to the specific constructions andarrangements shown and described, since various other modifications mayoccur to those ordinarily skilled in the art.

1-3. (canceled)
 4. A method for operating a medical robotic system,comprising: commanding a robotic arm to move a surgical instrument abouta pivot point in response to movement of an input device; determiningwhether the pivot point moves more than a threshold value; andcommanding the robotic arm to stop movement of the surgical instrumentabout the pivot point if the pivot point moves more than the thresholdvalue.
 5. A method for operating a medical robotic system, comprising:commanding a robotic arm to move a surgical instrument about a pivotpoint in response to movement of an input device; determining whetherthe pivot point moves more than a threshold value; and issuing a warningif the pivot point moves more than the threshold value.